Magnetic transducing system



l5 R. K. POTTER 29531942 MAGNETIC TRANSDUCING SYSTEM Filed om. 3o, 1947 2 sheeis-sheet 2 /5j FIG. 3A SIG/VAL EMS/NG 9 5 SOURCE SOURCE f4 8 "it D/ELEcm/c f of? j MA @NET/c 6 .m I

sfo/VAL 5ms/Nc ou TPU?" O\ H6' #A 2, soz/RCE .SOURCE I 2422 /5 /7 /A/r/WTOR R. K. PO TTER Patented Nov. 28, 1950 MAGNETIC TRANSDUCING SYSTEM Ralph K..Potter, Morristown, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application October 30, 1947, Serial No. 7 83,057

9 Claims. (Cl. 179-40055) This invention relates to the modification of time-Varying functions in accordance with preselected patterns; more particularly, it relates to electrical transducers of the types which are known in the art as transversal filters.

Thebehavior of electrical networks can be specied in two ways representing two different physical points of View. Ordinarily, one thinks first of the well-known steady-state point of view which describes the network performance in terms of the concepts of amplitude and phase response versus frequency. In addition to this more conventional viewpoint there is the time function viewpoint in which the network is described in terms of its amplitude time response at the receiving end resulting from the application of an impulse of infinitesimal duration at the sending end. Network response may thus be considered either in terms of frequency or time functions. The bridge between these two avenues of approach is the Fourier integral which may be thought of as a mathematical device for expressing a time function in terms of steadystate phenomena.

For the most part prior art practice has been to base the design of communication networks upon the steady-state frequency-amplitude characteristics and an elaborate theory has been worked out for such design procedures. The networks thus obtained contain as elements, resistances, inductances and capacitances, the frequency and/or phase selective effects of which are used in various combinations to secure desired response characteristics.

On the other hand, when network design is considered from the time function point of view, that is when time rather than frequency is taken as the independent variable, one is led to a broad group of selective circuits whose principle of operation does not depend upon resonant combinations of network elements.

Selective circuits embodying the time-function concept have been disclosed in Patents 2,024,900, December 17, 1935, 2,124,599, July 26, 1938, and 2,128,257, August 30, 1938 to N. Wiener and Y. Lee; in application Serial No. 731,232, led February 27, 1947, by L. C. Peterson and R. K. Potter and elsewhere in the art.

It is the principal object of this invention to provide certain improvements inthe art of modifying given functions of time in accordance with desired patterns of amplitude, frequency, and phase variation.

A more specific object of this invention is to utilize magnetic recording and reproducing techniques and apparatus for modifying an impressed electrical input in accordance with a preselected admittance function.

A certain class of devices, known in the art as transversal filters, substitute the time-function approach for the conventional steady-state approach in the simulation of network response, operating through a series of steps which include the following:

(1) Recording or storing theinput signal (2) Weighting the stored record in accordance with a predetermined multiplying function; and

(3) Integrating the weighted increments of record to produce a modified output The present invention relates to a transversal lter comprising a magnetic recording :and reproducing system.

The function to be filtered is recorded on a magnetic tape which is subsequently passed through a reproducing system having a plurality of spaced pick-up points. The amount of pick-up is varied from point to point over the pick-up interval in accordance with a predetermined' weighting function; and the weighted increments of current from the respective points are continuously summed to produce the desired ltered output current.

In accordance with one system of the present invention, a magnetic recording tape is progressively moved past a magnetic recording device comprising, a core longitudinally disposed with respect to the recording tape, and separated across the width of the tape into a plurality of alternate magnetic and non-magnetic sections or laminations which are cut by a laterally eX- tending air-gap adjacent to which the tape passes. A coil, comprising parallel wires joined at one end and connected at the other end to an electrical signal source, is substantially aligned above the air-gap so as to cut the separate nux paths of the magnetic sections of the core, whereby a multiplicity of substantially parallel records of the impressed signal are produced on the passing magnetic tape. The composite record so produced is passed through a reproducing device having a similarly subdivided core with a laterally extending air-gap, and a reproducing coil aligned thereabove, which coil is shaped in accordance with a predetermined weighting function to receive varying amounts of flux from the separate magnetic sections. The coil is coupled to an output circuit which serves to collect and integrate the increments of induced current. Either the air-gap in the `recording device or that in the reproducing device is disposed 3 at an oblique angle with respect to the direction of travel of the recording tape, so that each of the magnetic sections of the core in the recording device is adjacent at any one time to a point on the record representing a different instant in the history of the input signal.

Several alternative forms of the system are described.

Other objects and features ofj the present invention will be understood from a study of the detailed specification hereinafter and the at-- tached drawings, in which:

Figs. 1(A) to ME) present a series of diagrams illustrating the theory of operation of trans-- versal filters;

Figs. 2(A) and 2(B) show graphs'of two 'spe-w cic 'filter characteristics;

Fig. 3(A) shows a composite magnetic recording device operating on a moving magnetic tapel at a plurality of points disposed obliquely with respecty to its length;

Fig 3 (1B) shows an energizing :.coil adapted. for4 insertion in the upper gap ofsthe Aunit shown in Fig. 3(A);

Fi'gr3lC) lshows a plan View of theunitl'shown .er

Fig. 46A) shows-ay composite reproducing v.dea-v Fig. LUB)- shows 'an energizing coil adapted for insertioninthe uppersgap ofthe unit' shown in Fig. LMA), whichfrisl so designed as to'vary the magneticinduction-'atvthe respective pointsA of operation in--accordance with a predetermined:

weighting function;

Fig.-4 (C)`V shows a -planview of theunitshown in Fig-.4(A); and

Fig- 4 AD fshows A'the-curve of a typicalweighting function utilizedito shape the reproducing coil-Eil of Figs. 46A) and.^:(B).`

A concept=wl-iichmay -be helpfulin interpreting. r the specification and claims hereinafter is` :that of the transferindiial admittance of asystem. This' Quantity:isv definedby J. R. Carson inElec tric Circuit Theory and the Operational: Cal-v onlus',- McGraweHill, 1926,-'1page` 14,. as lthe-ratio of theoutput Ycurrent-of the system,-V expressed-as a ltimefunction?-to the -magnitudetof 'the steady v electromotive-fo1ce suddenly 'inserted ati-the putof the system at timet=`9f Thel time-rate-of-change of the transfer in-'` n dicial Y admittance `defined aboveis a function of timefdesignatedfgw) The function g t is variousiyreferred to in thespeciicationfand claims Further .discussion and idenition of -v certainf.`

function point .of view is based arerillu'strate'd inigsd (1A) to"1 E)-, to which reference Vis now:

inadew Consider a frequency selective Vnetworki.

suchasis illustrated.schematically by N in Fig... UA). wave E(t).1 shownin Fig. 105)y which.; is anyY 'conf` tinucus. function. of. voltage versus. times-.is .innI

pressedfuponthe.=input .l ofthe networks; At.I

lie-output Zithere :willthen appear a-current:

Letzus. assmnethat the complex voltage.-

wave which we designate as IU). Now let it be supposed that the voltage wave E05) is split up into a series of narrow pulses as shown in Fig. MC). With this pulsed wave impressed upon the input terminals I, one should expect to obtain at the output terminals 2 very nearly the same current wave I(t) obtained before.

Now'referring to Figc; lQD'J, assumethat there is impressedfupon the network a singlel pulse of the sort into which the voltage wave E(t) has been subdivided. At the network output termnals.2 there .now appears a function which as the pulse width approaches zero is proportional tothe gsf-unction of the network as deiinedvabcve.` It should be noted that any other pulse' of differentamphtude results in the same approximate gffunction except that its arnplitude varies in proportion to the applied pulse amplitudeand that moreover its time of occurrence depends on the time of pulse application. Thus lit; followsfas'shown iniEig. 16e) that in'uthe limitxtheicurrent wave :-I (t) whichrappears attheff outputpterrninals 2 as auresult offtheapplications ofitthervoltagerwave Ett) rat. the input terminal-. i is the sumotainumber of .overlapping"g,func tions? whose relativestrengths or amplitudes vary inrzacccrdance with 'tha-impressed voltage. wave f E (D1. Using somewhat `more r-iprecise Vlane guagerone can'say vrthat .if thenetworlre iswsuoejec-tedzat thesinput 'i to an. initial pulse'at soma: arbitrary time,=..which for' convenience may` loe-eA called zero,.and if this pulse is followed-byfothers at specified values oftimeythe .totallresponsewatn the Loutput terminals 2 at any later time .willbef thefsum of the responses which :have occurredv.; up to-that time.

Thus two .importantf'fprinciples -applicabletd-r this approach to networktheory may bev derived'f.- from -.the above.. First, ,thenetwork-responseto.` unit impulse vof nnitesimal durationV complete.1v lyA determines the ,response :.to any ,f other .input wave econd, .,theresponsefat anytime-1dependsuponthe yhistory of the applied input wave'p previous to the time in question so'thatfthe. past. history fmust be ravailable at least. over .ai time interval 'withinfwhichf the 1gl-:functionv iswofff appreciable magnitude..4

Therefore the network fcan be loo-kedeuponz; asA acircuit for#eifectingthezsummation of a'4 series of time displaced- .g.functions inf which thek individualampiitudezof each of .the respec--f tice` g-functionsf istproportional to the-cor-vv responding itime-:displacedl l:instantaneous value of the impressed voltage wave-Etz); YThis..pro`c:'; essislschematically indicated...in. Fig.. 1(E`) Adopting a slightly differenty point of view'- one? can also -lookupon the output wave as representing at- -any 'time -a weighted history orvrecordof the input-wave where the gr-"functionthas-acted-` as the Weighting factor.r

The foregoing statements may be summarized"y by deriving'a mathematical 'expression'for' the' network .response to' anl arbitrary driving force from vthe assumptionthat thenetY .behavior of...v a linear.- -systemat anyin'stant is...a.fu`nction` of.v the linear superpositionwof all the responses..V Which have occurred up to .that time mounting.. from.some -larbitrary startingu point. Assume, for example, that a'networkis subjected Ytovan` initial voltage pulse EG). 'at the-timevt :'-0 andraY that this pulsexis' followedrby others .atwspecieda values of time. Then the total responsefat" anyfz later time will bethesum ofthe responses: which have occurred 'up to# that. :timefdue`A allowance@v` being made for the time at which ach pulse was applied.

Let the time axis then be divided into short intervals Ar of equal width, the electro'motive force EG) being approximated by a series of rectangular pulses applied for the duration of each time interval Af. The total response at a specified time t is thenfapproximately the sum at that instant of all the elementary responses started previous to that instant. If the interval A-r is very small, that is, approaches zero as a limit, the response at time t to the first impulse is ArE(0)g(t), where g(t) is the response to unit impulse or g-function" as defined hereinbefore, and where E(O) is the amplitude of the voltage Wave E(t) at time t=0. Consider now the (n+1)th impulse. The response at time t is E(nAr)Arg(t-nA1-). In this expression it should be noted that nm is the time of impulse application. The reason that the argument of the g-function in this latter expression is t-nAT and not t is that this pulse does not come into existence until the time mir and the expression is only valid for the time equal to or greater than uA-r. time scale to be denoted by T, thus i-=nAr- The current response I(t) at the instant t is the sum at time t of all elementary responses that have occured between time equal to 0 when the first impulse was started and time t as the length of Assume an arbitrary point on the the time interval AT approaches zero. Hence t Matre) TEcmfgo-f) (i) By definition of an integral this may also be f written .A I(t)=JXE(r)g(t-r)dr (2) i(i)=f)tE i-1)g()df (2') This equation thus expresses the system response to an arbitrary driving force in terms of the response to a unit impulse, that is, an applied pulse which in the limit approaches unit area and infinitesimal duration. Thus it follows that a knowledge of the response g(t) to a unit impulse is suflicient to specify completely the system performance. This implies in particular that the steady-state performance of a particular network may also be determined from a knowledge of g(t) for that network. Suppose, for example, that the network is a lter passing a certain band of frequencies. merely a reflection of the fact that g(t) behaves ina very definite manner. To illustrate this in a general way, assume that a sinusoidal voltage E(t)=E sin wt, where E represents the steadystate amplitude and w=the angular frequency, has been applied to the network at 15:0; and that all transients have died out. The steadystate current can then be written as IU) =EiY12(iw)l Sin [wi(w)]= Eeuw) sin wid-Ehem) cos wt (3) where Yi2(iw) is the transfer admittance between input and output terminals of the selected network and @(w) its phase angle. By writing Yi2(iw) =ai2(w) -l-ibiz(w), in which aiz and biz are constants, the second of expressions (3) is obtained. An equivalent expression may also be obtained from (2) or (2') by inserting En?) =E sin it This is then and extending the range of integration to infinity (which means that transient distortion has out) one obtains,

Ic) :E sin ai Lw @0S algem- E COS cui La) Sin oJTg TDd1` By comparison of (3) and (4) it follows that The points to be emphasized in general are, first,

that the Expressions 5 establish quantitativev relations between the frequency selection properties of the networks and the response to unit impulse excitation; and second, that both the real and imaginary components of the transfer admittance can be calculated from a knowledge of the response to unit impulse. This relationship may also be further illustrated as follows: Multiply the second of Equations 5 with i, the Imaginary unit, and add to the first; then use Eulers formula. The result is from which it follows that the steady-state transfer admittance is the Fourier transform of the unit impulse response. point of View, it is thus irrelevant whether frequency selection properties of a network are stated in terms of steady-statefrequency `response to sinusoidal driving forces or whetherl they are given as the time response to a unit impulse. The frequency response is merely the spectral analysis of the time response to a unit impulse. It also follows from (6) that thigh/dwp COS [ml-@wide y (17) where Y12(iw) denotes the amplitude and @(w) the phase of the steady-state transfer admittance. Equation '7 in principle allows g(t) to be calculated from a knowledge of the frequency spectrum of the steady-state transfer admittance, i. e., from the amplitude frequency and phase characteristics of the network. Moreover, We have from (5) QU) La) (112(60) COS cotdw and (8) 9 (i) L bmw) siii wid@ Hence it follows that the time response z2/(t) to unit impulse is completely determined when either the real or the imaginary component ofV the steady-state transfer impedance is specified over the entire frequency range.

Stressing the physical interpretation of the facts presented rather than the mathematical analysis, three steps are suggested by means of which an applied input function may be modied in accordance with certain admittance characteristics to produce a desired output response without resort to the conventional concepts of frequency selective networks. They are:

(l) Recording or storage of the input wave; (2) Weighting of the stored record by means of selected g-functions; and

(3) summation of theweighted record.

died

From a principaldesinee These 'are `fundamental steps which `cart serve as building blocks in frequency selective devices operating on a time-function basis. It `should be noted that in arriving at these steps no reference has been made tovibrating systems such -as coil and condenser combinations nor has any use been made of the concepts of amplitude and phase versus frequency response. These concepts have now been replaced by kthe single 'con'- cept of the g1-function. In other words, the physical phenomena conventionally vdescribed by the amplitude and phase 'versus frequency functions are now described by the single function g(t).

As concrete examples of g1-functions, consider two cases of functions in which the positive and negative values are symmetrical with respect to a certain Val-ue of time, say time To, where To 0. Consider iirst allow-pass filter having a uniform transfer impedance equal to K from frequency zero to a cut-off frequency we. Outside this range it its assumed -that no transmission occurs. As a consequence of the stipulation of even time response, the phase shift @(wf) is linear and is given by the following'equation:

For the low-pass lter under consideration there is obtained a particular g-function,

which will be designated 17105), by substituting the above conditions in Equation '7 which relates to the generalized function g(t), and integrating the expression over a fchosen range of angular.

frequencies from zero to we.

demonstrated that the width of the main oscillatory lobe is inversely proportional tothe band width fc. It is also seen that the received signal reaches its maximum at the time t=T and that the maximum response is proportional to the area waK under the amplitude characteristic.

As a second example we lconsider an idealized band-pass filter of even time response and with a fiat amplitude characteristic between the cutwhich may bereduced to Here w represents the band width ecol-wc, and wm the arithmetic mean of the two cut-off frequencies wel and vez and may thus be considered to coincide with the mid-band frequency. Equation 11 which is roughly plotted on Fig. 2(B) represents an amplitude modulated carrier wave cos emu-Tol 11) S with 4a carrier frequency equal to that of midband. The maximum response occurs at t'=Tn and 'proportional to wK which is the area under "the amplitude response characteristic andV the length lof the main oscillatory lobe is which lis inversely proportional to the band width.

The examples selected show that several important properties of the steady-state characteristics can be obtained directly `from an in* spection of the plots of the g-functio'ns. ltmust be emphasized, however, that too much signi-flcance cannot be attached to the calculated "ifunctions since th'eyare based uponassumptio'ns which cannot be realized. On the other hand, the general A"qualitative and quantitative properties of rthe gr-functions for the lters in question are believed to have `been preserved, althoughone is notl justified in attachingtoo much significance to any 4of 'the finer details.

The computation Aof the g1-function," as discussed hereinbefore, has necessarily been in "broad general terms, with several specific applications by way of illustration. From the 4previous, 4discussion, the Aprocedure will be apparent to kthose skilled in the art for uniquely 'computing "'gfunctions to comply with specific sets of conditions imposed in other particular casesthantho'se discussed.

In accordance with the present invention, the functions outlined hereinbe'fore, namely, (l) recording or storage of the input wave, (2) weighting of the stored record by means of selected gy-functions, and (3) summation of the weighted record, are carried out in a system comprising magnetic recording and reproducing units operating simultaneously at a plurality of separate points on a moving magnetic tape.

in a preferred embodiment, elements of which are shown in Figs. 3A, 3B, and 3C, and Figs. 4A, 4B, an'd 4C, the magnetic tape is moved past a pair of composite recording and reproducing devices, each of which c'oinpr'is'es a single Vcomplex unit adapted t'o simultaneously operate on the 'tape magnetically at a multiplicity lof points. The recording device, 'shown 'in the typical embodiment of Fig. 3A, comprises a pair of polepiec'es longitudinally disposed with respect t'o Vthe' moving tape so as to substantially form a hollow parallelepiped, the base of which is vadjacent the surface of the moving tape and extending obliquely thereacross. For the purposes of illustration, the tape Vmay be Aassumed to be moving in a horizontal plane. The taperedv tape contacting members of the pole-pieces are separated by a narrow air-gap which extends obliquely acrossthe width of the tape, aligned above which is abroader `gap or recess between the upper portions of the pole pieces, Vinto which isntted a shaped element containing the recording coil. By means of a series of vertical planar non-magnetic separating elements, which extend parallel to the length of the tape the pole-pieces are divided across the width of the tape into a plurality of separate magnetic circuits, each responsive to operate on a diiferent section of the moving magnetic tape.

Fig. 3B shows in perspective ythe element containing the recording coil which comprises a matrix element shaped to fit into the obliquely extending upper recess between the pole-pieces. Moulded into the matrix element in a plane aligned with its long dimension is a pair of substantially straight parallel wires which are joined at one end to form a loop, the open end of which is coupled to the input signal source as shown in Fig. 3A.

Fig. 3C shows a plan View of the recording device of Figs. 3A and 3B. On the magnetic tape emerging from the device are indicated a plurality of longitudinally displaced records of the impressed input function. Y

The magnetic reproducing device shown in Fig. 4A comprises a pair of longitudinally disposed magnetic pole-pieces in contact with the moving magnetic tape from the recording device of Fig. 3A, and divided into a corresponding number of vertical planar magnetically responsive sections or laminations across the width of the tape. The reproducing device is similar in form to the recording device of Fig. 3A, except that the tape contacting base thereof is rectangularly shaped, so that the lower gap between the pole-pieces extends across the width of the tape normally to the direction of motion and the reproducing coil mounted in the upper gap is critically shaped as shown in Fig. 4B.

Fig. 4B shows a sectional view of a typical vertical-planar reproducing coil long enough to embrace all of the magnetic laminae, which is mounted in a matrix element similar to that of the recording coil of Fig. 3A, and which comprises a pair of wires bent into a series of loops in a vertical plane, the respective vertical dimensions of the loops corresponding to the coordinatesof a chosen weighting function. The reproducing coil of Fig. 4B in its shaped matrix element is mounted in the upper gap between the pole-pieces of Fig. 4A as shown.

Fig. 4C shows a plan View of the reproducing unit operating on the multiple-record magnetic tape which is moved past its contacting base members at a uniform rate, whereby weighted increments of current are induced in different portions of the looped reproducing coil and continuously integrated in the output circuit producing output current ltered in accordance with a desired characteristic.

Referring in detail to Fig. 3A of the drawings, the recording tape I comprising a paramagnetic material such as stainless steel, having a width of several inches, and a thickness of the order of a few thousandths of an inch, is moved at a uniform rate from left-to-right across a given space interval by conventional means, such as, for example, the toothed wheels 2 and 3 which are synchronously driven by driving means, not shown, to rotate in a clock-wise direction operating on peripheral notches in the tape I. For con venience of description, it will be assumed that the tape I is moving in a horizontal plane, and the other elements of the system will be described as assuming positions relative to a horizontal position of the tape, on which they will be assumed to have their bases.

The magnetic recording unit of Fig. 3A coinprises two laminated polepieces 4 and 5 about an inch high, which are formed with inwardly extending flanges at the upper and lower ends, whereby their cross-sections are C-shaped. In each of the pole-pieces 4 and 5, the edges of the bases in contact with the tape I are in acute angular relationship, whereby, when the units are combined they substantially form a hollow parallelepiped extending obliquely across the width of the tape I, the lower inwardly extending flanges thereof being tapered to include an ob- `depth of the order of one-eighth of an inch, the

upper recess I2 being aligned over the lower gap II.

The pole-pieces 4 and 5 are subdivided across the width of the tape along A,the gap Il and the recess I2 into an equal number of vertical magnetically responsive sectionsor laminae 6 and 'I, comprising for example, soft iron by non-magnetic separating sections or laminae, 8 and 9,

comprising for example, brass. The magnetic and non-magnetic sections 6, l, and 8, 9 have equal width dimensions of a fraction of an inch each, so that the over-all dimension of the recording unit across the tape, depending on the number of sections, is of the order of two inches, and the over-all dimension along the tape is of the order of one inch.

Fig. 3B shows a perspectiveV View of a matrix element I3 which nts into the recess I2. The matrix I3 may comprise either magnetic or nonmagnetic material in which is embedded the recording coil I li, comprising parallel wires forming a loop, which extends somewhat beyond the length of the recess I2. As shown for clarity, the coil I i may comprise a single loop or, preferably, many windings. In either case the shaping of the coil should be maintained so that the area r enclosed is substantially a parallelogram disposed in a vertical plane aligned with the long edges of the matrix element I3. The open end of the coil I4 is coupled through the transformer I6 to the signal source I5, which may comprise a conventional generator of .electrical signal current having a characteristic which varies as a function of time, on which it is desired to impress modifications in accordance with the teachings of the present invention. The biasing circuit I'I, which is connected in parallel with the signal source I'I, represents a conventional generator of oscillating biasing current, which has a frequency of the order of two or three times the highest frequency of the signalling source I5, and which when superposed on the input signal has the eiect of increasing the linearity of response of the reproducing system.

From the plan View of the recording system shown in Fig. 3C, Vitis seen that a plurality of parallel spaced records I, II, III, and IV corresponding to the number of magnetic recording elements, are produced, such that points a, b, c, and d, representing identical instants in the history of the impressed input function appear in oblique relation across the width of the tape i.

The tape I, bearing the multiple records of the input function impressed from the signal source I5, is passed at a uniform rate through a magnetic reproducing system, such as will be described in detail with reference to Figs. 4A, 4B

and 4C of the drawings. The tape I of Fig. 4A, which may be considered to be an extension of the tape l of Fig. 3A, is driven by the toothed wheels I8 and i9 which are driven synchronously withlthe toothed wheels 2 and 3 of Fig. 3A.

The magnetic reproducing unit of Fig. 4A,

which is disposed with its base adjacent the moving tape I, comprises laminated pole-pieces 20 and ZI, which are sub-divided into respective magn and non-magnetic sections or laminae gap 26 adjacent the recording tape, and the coaligned upper recess 2,1 extend across the widthv of. the, tape in a direction substantially normal tothe length of the tape I.

Fig. 4B shows in side elevation a matrix element 2.8` Whichtsinto the recess 21, and which may comprisev either magnetic or non-magnetic material.. suchas the, element I3, of Fig. 3B. In a verticalA plane parallel to the long dimension of the element 28 is embedded the reproducing coil, 2,9. The coil 29 is formed into a series of loops the verticaldimensions of which respectively vary in accordance with the ordinates of a chosen g-functionf The form of the coil 2B, asV shown by way of example, corresponds to a typical g-function such as shown in Fig. 4D, andthe form of,A which is computed in accordance with the teachings set forth in the early part ofthe specification. The respective wires are insulated from one another at each point of.v crossover. It is noted that the relative posi tions of the input and output wires in each of the loops determines the polarity of the induced current whereby the recording unit is adaptn ed. to utilize weighting functions having components of either or both signs. The open end ofthe coil 29 is` connected through the transformer 3l to the output terminals 3B.

The plan view ofv Fig. 4C shows the assembled .reproducingsystem,v including the tape l bearing, a plurality of' parallel magnetic records I, II;` III, and IV of.' the input function, which correspondin number to the separate magnetic circuits in the recording and reproducing de vices, and which are displaced` in time, so that the points a, b, c and d, representing identical increments of the impressed input signal are fed through the gap 2li obliquely arriving at different instants in. succession.

Assume that theY signal ateach of the points a., b, c and dv on the identical parallel records I, II, III and IV is represented by E (to) and that an interval of' timeV t=AT is required for the magnetic tape l to move from a position in which point a on record I is adjacent the gap 2EV to a position in which b on record II' is thereadjacent; and, moreover, assume that a time interval; TY=4AT, representing the time duration of the chosen gv-function, is required for the projected distance from a. to d to be traversed by the motion of the tape. I.

Assume also, that the coil 29.. representing the function g(t) isso` positioned, in the gap 2l. that its vertical cross-sectional dimension directly above. record No.1 is 9Go), above record No. II is. Q,(AT=)., above record; No. III is g(2AT), and above record No. IV is, gtn'l).

If the instant when a is adjacent the gap 2@ is selected as 12:0; thenA the magnetomotive forces impressed on eachv of the respective magnetic circuitsy by4 the moving tape i at that instant are as follows:

Byrecord No. II, Mn-.g-Etto-AT); By record. No. III, Mm=E(tn-2AT) and By record 1\To..IV,` M1v=E(tu-3AT).

Therefore, the current induced in an element AT of the coil 29 by each of the respective magnetic circuits is as follows:

Now if the output currents represented above are summed and the sum presented in generalized terms indicating a recording and reproducing system having n magnetic circuits, the total out put current at time t=0 may be represented as follows:

In the above equation, T varies through integral values from 0 to unf, where mir is the period required to completely represent theV chosen g-function.

It is thus seen that the output current at. each instant represents an approximation of. the re.- sponse integral cf the form given. in Equation 2 in the early part of the specification.. It is thus apparent that the magnetic recording and reproducing device describedV in the foregoing paragraphs can bel constructed in such form as to simulate the transfer impedance of any chosen network, if the recording coilV 29 is constructed to represent the r1-function corresponding to the desired admittance characteristic. Although in order to simplify description the recording and reproducing units of Figs. 3A and 4A have been disclosed as each comprising only four magnetic circuits, a practical system in accordancewith the present invention would preferably comprise many times that number.

Assuming that the velocity of the recording operaticnis equal to the velocity of the reproducing operation, the Obliquity of the air-gap Il and the recess l2 in the recording device of Fig. 3A, should be such that the projected distance along the edge of the tape between points c and 0l is preferably made at least equal to m, the duration of the chosen cf-function. Moreover, if the ratio of the reproducing velocity te the recording velocity is other than unity, the projected distance X between points a and d should` pref-- erably be made at least equal to. 1 multiplied by this, ratio.

The principles of the invention may be equally Well applied to a systemz in which the recording gap il and the recess l2 are disposed at right angles to the direction of motion of the tape, and the reproducing gap 26. and the recess, 2T are disposed obliquely with respect to the tape. It is also apparent that thesame resultant.- output current may be obtained by shaping the recording coil lli in accordance with the chosen g1-function instead of the reproducing coil 29, as disclosed.

Moreover, other variations of the invention will be apparent to those skilled in the art, such as. a system utilizing a single magnetic record of the input function which` is passed through. a kreproducing device having an air-gap disposed along the length of the tape, and operating at a plurality of pick-up points therealong.

From the foregoing discussion, it will be apparent that the principles of the present invention can be embodied in many other formsthan those specifically disclosed herein.

What is claimed is:

1, In a magnetic recording-reproducing sys-- tem in combination, a magnetic recording tape, an electromagnetic recording device which includes a core comprising alternate laminae of magnetic and non-magnetic material, said core constructed to include a pair of elongated gaps which cut a plurality of said laminae, driving means to progressively move said magnetic recording tape in transducing relation to a rst one of said gaps in said recording device, an electrical signal source, an elongated recording coil recessed in the second gap of said recording device with its major dimension in transverse relation to the magnetic laminae of said core, said recording coil disposed in flux linking relation to a plurality of said laminae, said recording coil coupled to said signal source whereby a plurality of magnetic records of said signal corresponding to the number of said laminae are impressed on said recording tape by said recording device, an electromagnetic reproducing device disposed to respond to the plural magnetic records of said tape, said reproducing device including a core comprising alternate laminations of magnetic and non-magnetic material, said core including a pair of elongated gaps which cut a plurality of said laminae transversely, said driving means disposed to vprogressively move said magnetic recording medium in transducing relation to the rst one of said gaps in said reproducing device, an elongated reproducing coil recessed in the second gap in said reproducing device with its major dimension in transverse relation to the magnetic laminae of said core, said reproducing coil disposed in ilux linking relation to a plurality of said laminae, and an output circuit in energy transfer relation with said reproducing coil.

2. In combination with a magnetic recordingreproducing system which includes a magnetic tape having a recording surface, a magnetic transducer operative on said tape which comprises a pair of elongated core members of C- shaped cross-section which form a hollow structure including a pair of elongated gaps extending in a direction transverse to the length of said tape, only one of said gaps disposed in transducing relation with said recording surface, said core members separated in said transverse direction into a multiplicity of separate magnetic circuits comprising laminations of magnetic material arranged in alternating relationship with laminations of non-magnetic material, said laminations disposed in a series of parallel planes substantially normal to the long dimension of said gaps, a matrix element dimensioned to fit into a second of said gaps and substantially coextensive therewith, an elongated coil substantially coextensive with the long dimension of said matrix element and inserted therein in flux linking relation to each of said magnetic circuits.

\ 3. A magnetic transducer in accordance with claim 2 in which the major axes of said gaps are obliquely dimensioned with respect to the direction of travel of said tape.

4, A magnetic transducer in accordance with 5. A magnetic transducer in accordance with claim 2 in which said matrix element is readily movable from said second gap.

6. A magnetic transducer comprising in combination a hollow core comprising a stack of alternately magnetic and non-magnetic laminae having two gaps therein extending through said laminae lengthwise of the stack and dividing the core into two portions, a magnetic recording ribbon, said core disposed with one of said gaps extending transversely across said magneticl ribbon in transducing relation therewith, and an electrical circuit disposed in the other of said gaps linking the ilux paths between juxtaposed ends of the several magnetic laminae in varying proportion and polarity.

7. A system in accordance with claim 1 in which an oblique angular relationship exists between the directions at which the gaps in said recording device and said reproducing device respectively extend across the width of said tape.

8. A system in accordance with claim 1 in which at least one of said coils is shaped to intercept substantially different amounts of flux adjacent diierent ones of the laminae in the respective core.

9. A filter system comprising an input circuit, an output circuit, a magnetic recorder and a magnetic reproducer disposed at spaced points along a movable magnetic record carrier in wave transducing relation therewith, said recorder comprising a unitary structure having a multiplicity of distinct portions all coupled to said input circuit and adapted to record at respectively different corresponding laterally separated points on said magnetic record carrier whereby an electrical signal appearing in said input circuit is simultaneously recorded in respectively corresponding laterally separated tracks along said magnetic record carrier, said reproducer comprising a unitary structure having a multiplicity of distinct portions all coupled to said ouput circuit and adapted to reproduce from respectively different corresponding ones of said laterally separated tracks, said reproducer portions being differently spaced from said recorder portions whereby the signal reproduced by each of said reproducer portions is in time-displaced relation with the signal reproduced by each of the other said reproducer portions, said coupling to at least one of said circuits being varied from one to another of said multiplicity of portions in accordance with a predetermined weighting function.

RALPH K. POTTER.

REFERENCES CITED rShe following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 2,195,192 Schuller Mar. 26, 1940 2,327,956 Begun Aug. 24, 1943 2,344,615 James Mar. 21, 1944 2,351,003 Camras June 13, 1944 2,354,176 Goldsmith July 18, 1944 FOREIGN PATENTS Number Country Date 693,956 Germany Aug. 24., 1943 

